Fluoropolyether compound, lubricant, magnetic disk, and method for producing same

ABSTRACT

Disclosed is a fluoropolyether compound comprising a C 4-10  aliphatic hydrocarbon chain present in the middle of the fluoropolyether compound and at least two perfluoropolyethers.

This application is a 371 of PCT/JP2015/082882, filed Nov. 24, 2015.

TECHNICAL FIELD

The present invention relates to a fluoropolyether compound, alubricant, a magnetic disk, and a method for producing the disk.

BACKGROUND ART

With the increasing recording density of magnetic disks, the distancebetween a magnetic disk serving as a recording medium and a head forrecording and reproducing information has become almost nil as theyapproach coming into contact with each other. The magnetic disk surfaceis provided with a carbon protective film and a lubricant film(lubricant layer) to diminish abrasion caused by contact with the heador sliding of the head thereon, and to prevent contamination of the disksurface. Specifically, these two layers protect the surface of themagnetic disk. In particular, the lubricant layer provided on the topmust have various properties, such as long-term stability, chemicalresistance, friction properties, and heat resistance, andfluoropolyethers have been often used as a lubricant for magnetic disks(e.g., Patent Literature 1 and 2).

Recent years have seen the development of a technique called“heat-assisted magnetic recording” (HAMR), which aims to increase therecording density of magnetic disks. In HAMR, a recording spot is heatedby laser irradiation immediately before writing. The heating temperaturereaches 300° C. or more, and the lubricant on the magnetic disk isexposed to high heat. This evaporate, and the lubricity may not bemaintained.

To prevent the evaporation of the lubricant at high temperatures, it isimportant to enhance the adsorption of the lubricant to the surface ofmagnetic disks. Patent Literature 3 and 4, for example, have proposedtechniques to increase sites for adsorption to the magnetic disk byintroducing hydroxyl groups into the molecule. However, these techniquesare also still unsatisfactory in the bonds between the lubricant and themagnetic disk, and lubricants capable of forming stronger bonds withmagnetic disks have been desired.

CITATION LIST Patent Literature

-   Patent Literature 1: JP2009-301709A-   Patent Literature 2: WO2009/066784-   Patent Literature 3: JP2006-070173A-   Patent Literature 4: JP2010-086598A

SUMMARY OF INVENTION Technical Problem

An object of the present invention is to provide a fluoropolyethercompound, a lubricant, and a magnetic disk that have such an excellentheat resistance as to be able to maintain the lubricity of the magneticdisk surface, without evaporating at high temperatures under laserheating, and also to provide a method for producing the disk.

Solution to Problem

The present inventors conducted extensive research, and found that theuse of a fluoropolyether compound comprising an aliphatic hydrocarbonchain having a specific number of carbons and at least twoperfluoropolyethers, each perfluoropolyether being ether-linked to thealiphatic hydrocarbon chain can achieve the object. The presentinvention has been completed on the basis of the findings.

The present invention relates to fluoropolyether compounds and the likedescribed in the following Items 1 to 7.

Item 1.

A fluoropolyether compound comprising a C₄₋₁₀ aliphatic hydrocarbonchain present in the middle of the molecule and at least twoperfluoropolyethers, each perfluoropolyether being ether-linked to theC₄₋₁₀ aliphatic hydrocarbon chain,

the aliphatic hydrocarbon chain having at least one hydroxyl group,

the at least two perfluoropolyethers having, at respectivenon-hydrocarbon chain terminals, at least one polar group selected fromthe group consisting of —OH, —OCH₂CH(OH)CH₂OH,—OCH₂CH(OH)CH₂OCH₂CH(OH)CH₂OH, —O(CH₂)_(m)OH, and—OCH₂(OH)CHCH₂—OC₆H₄—R¹ wherein m is an integer of 2 to 8, and R¹represents hydrogen, C₁₋₄ alkoxy, amino, or an amide residue.

Item 2.

The fluoropolyether compound according to Item 1 wherein the aliphatichydrocarbon chain has 8 carbon atoms.

Item 3.

The fluoropolyether compound according to Item 1 or 2 which is at leastone member selected from the group consisting of

HOCH₂CH(OH)CH₂OCH₂CF₂CF₂O(CF₂CF₂CF₂O)_(z)CF₂CF₂CH₂—OCH₂CH(OH)CH₂CH₂CH₂CH₂CH(OH)CH₂O—CH₂CF₂CF₂O(CF₂CF₂CF₂O)_(z)CF₂CF₂CH₂OCH₂CH(OH)CH₂OH,

HOCH₂CH(OH)CH₂OCH₂CF₂CF₂CF₂O(CF₂CF₂CF₂CF₂O)_(w)CF₂CF₂CF₂CH₂—OCH₂CH(OH)CH₂CH₂CH₂CH₂CH(OH)CH₂O—CH₂CF₂CF₂CF₂O(CF₂CF₂CF₂CF₂O)_(w)CF₂CF₂CF₂CH₂OCH₂CH(OH)CH₂OH,

HOCH₂CF₂CF₂O(CF₂CF₂CF₂O)_(z)CF₂CF₂CH₂—OCH₂CH(OH)CH₂CH₂CH₂CH₂CH(OH)CH₂O—CH₂CF₂CF₂O(CF₂CF₂CF₂O)_(z)CF₂CF₂CH₂OH,and

HOCH₂CF₂CF₂CF₂O(CF₂CF₂CF₂CF₂O)_(w)CF₂CF₂CF₂CH₂—OCH₂CH(OH)CH₂CH₂CH₂CH₂CH(OH)CH₂O—CH₂CF₂CF₂CF₂O(CF₂CF₂CF₂CF₂O)_(w)CF₂CF₂CF₂CH₂OH.

Item 4.

The fluoropolyether compound according to Item 3 wherein z is a realnumber of 0 to 30, and w is a real number of 0 to 20.

Item 5.

A lubricant comprising the fluoropolyether compound according to any oneof Items 1 to 4.

Item 6.

A magnetic disk comprising, in sequence over a substrate: a recordinglayer, a protective layer, and a lubricant layer,

wherein the lubricant layer is formed by applying the lubricantaccording to Item 5 to the surface of the protective layer, andperforming ultraviolet irradiation or heat treatment.

Item 7.

A method for producing a magnetic disk that comprises in sequence over asubstrate, a recording layer, a protective layer, and a lubricant layer,the method comprising

forming the recording layer and the protective layer over the substratein this order,

applying the lubricant according to Item 5 to the surface of theprotective layer, and

performing ultraviolet irradiation or heat treatment to form thelubricant layer.

Advantageous Effects of Invention

In the fluoropolyether compound according, to the present invention, atleast one hydroxyl group contained in a C₄₋₁₀ aliphatic hydrocarbonchain present in the middle of the molecule and at least one polar grouppresent at respective non-hydrocarbon chain terminals of theperfluoropolyethers can bond to the surface of magnetic disks. Inaddition, the bonds between the carbon atoms of the C₄₋₁₀ aliphatichydrocarbon chain and the oxygen atoms are cleaved by ultravioletirradiation or heat treatment, and firm bonds are formed with thesurface of a magnetic disk. This reduces or prevents the evaporation ofthe compound by heating, and maintains the lubricity of the magneticdisk surface.

Thus, a lubricant comprising the fluoropolyether compound according tothe present invention can maintain the lubricity of the surface ofmagnetic disks at high temperatures under laser heating.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional diagram illustrating a magnetic diskaccording to the present invention.

DESCRIPTION OF EMBODIMENTS

In the fluoropolyether compound according to the present invention, aC₄₋₁₀ aliphatic hydrocarbon chain present in the middle of the moleculeis ether-linked to at least two perfluoropolyethers, and the aliphatichydrocarbon chain has at least one hydroxyl group. The at least twoperfluoropolyethers each have, at their non-hydrocarbon chain terminals,at least one polar group selected from the group consisting of —OH,—OCH₂CH(OH)CH₂OH, —OCH₂CH(CH)CH₂OCH₂CH(OH)CH₂OH, —O(CH₂)_(m)OH, and—OCH₂(OH)CHCH₂—OC₆H₄—R¹ wherein m is an integer of 2 to 8; and R¹represents hydrogen, C₁₋₄ alkoxy, amino, or an amide residue.

The aliphatic hydrocarbon chain present in the middle of the moleculehas 4 to 10 carbon atoms, preferably 4 to 8 carbon atoms, andparticularly preferably 8 carbon atoms. In the present invention, it isan important feature that the aliphatic hydrocarbon chain has 4 to 10carbon atoms. In the case of an aliphatic hydrocarbon chain having 4 ormore carbon atoms, ultraviolet irradiation or heat treatment cleaves thecompound between the carbon atoms of the C₄₋₁₀ aliphatic hydrocarbonchain and the oxygen atoms, and CH₂ at each terminal of the hydrocarbonand/or oxygen atoms (O) remaining in the perfluoropolyethers aftercleavage can firmly bond to a magnetic disk.

The aliphatic hydrocarbon chain encompasses both linear and branchedchains. In the case of a linear hydrocarbon, both terminals of the chainare linked to respective perfluoropolyethers through respective oxygenatoms. In the case of a branched-chain hydrocarbon, both terminals ofthe main chain and the terminal of at least one branched chain can beether-linked to respective perfluoropolyethers. When the number of thebranched-chain is, for example, 1, the hydrocarbon can be ether-linkedto 3 perfluoropolyethers. When the number of the branched-chain is 2,the hydrocarbon can be ether-linked to 4 perfluoropolyethers.

Perfluoropolyether skeletons typically used in lubricants for magneticdisks can be used for the perfluoropolyethers, without any limitation.The perfluoropolyethers, are a portion represented by, for example,—CH₂(CF₂)_(p)O(CF₂O)_(x)(CF₂CF₂O)_(y)(CF₂CF₂CF₂O)_(z)(CF₂CF₂CF₂CF₂O)_(w)(CF₂)_(p)CH₂—wherein x and y are each a real number of 0 to 30; z is a real number of0 to 30; w is a real number of 0 to 20; and p is an integer of 1 to 3.Here, x and y are each preferably a real number of 0 to 12, and morepreferably a real number of 2 to 8. When x and y are both a real numberof 2 to 8, the molecular chain becomes flat, providing a lubricant thatcan form a thin film; thus, it is preferable that x and y are both areal number of 2 to 8. Here, z is preferably a real number of 1 to 12,and more preferably a real number of 2 to 8. When z is a real number of2 to 8, the molecular chain becomes flat, providing a lubricant that canform a thin film; thus it is preferable that z is a real number of 2 to8. Here, w is preferably a real number of 0 to 10, and more preferably areal number of 1 to 5. When w is a real number of 1 to 5, the molecularchain becomes flat, providing a lubricant that can form a thin film;thus it is preferable that w is a real number of 1 to 5. Here, p is aninteger of 1 to 3.

Each of the non-hydrocarbon chain terminals of the perfluoropolyethershas at least one polar group selected from the group consisting of —OH,—OCH₂CH(OH)OCH₂OH, —OCH₂CH(OH)CH₂OCH₂CH(OH)CH₂OH, —O(CH₂)_(m)OH, and—OCH₂(OH)CHCH₂—OC₆H₄—R¹ wherein m is an integer of 2 to 8; and R¹represents hydrogen, C₁₋₄ alkoxy, amino, or an amide residue. The atleast one polar group is a functional group that interacts with thesurface of magnetic disks. The at least one polar group is weakly bondedto the surface of magnetic disks before ultraviolet irradiation or heattreatment, but can be firmly bonded to the surface when exposed toultraviolet irradiation or heat treatment.

The compound according to the present invention can be obtained, forexample, by reacting an aliphatic hydrocarbon having two epoxy groups(A) with a linear fluoropolyether having a hydroxyl group at oneterminal and a hydroxy-containing alkoxy group at the other terminal(a), or a linear fluoropolyether having a hydroxyl group at eachterminal (d). Specifically, the compound can be synthesized by thefollowing method.

[1] First, fluoropolyether (a) is synthesized (first step).

A linear fluoropolyether having a hydroxyl group at each terminal (b) isreacted with a compound that reacts with hydroxyl groups to form ahydroxy-containing alkoxy (c). The reaction temperature is 20 to 90° C.,and preferably 60 to 80° C. The reaction time is 5 to 20 hours, andpreferably 10 to 15 hours. The amount of compound (c) for use ispreferably 0.5 to 1.5 equivalents relative to fluoropolyether (b). Thereaction product is then, for example, purified by column chromatographyto obtain fluoropolyether (a). The reaction may be performed in asolvent. The solvent for use includes t-butyl alcohol, dimethylformaldehyde, 1,4-dioxane, dimethyl sulfoxide, and dimethylacetamide.The reaction may be performed using a reaction accelerator. Examples ofreaction accelerators include basic compounds, such as sodium, potassiumt-butoxide, and sodium hydride.

Fluoropolyether (b) isHOCH₂—(CF₂)_(p)O(CF₂O)_(x)(CF₂CF₂O)_(y)(CF₂CF₂CF₂)_(z)(CF₂CF₂CF₂CF₂O)_(w)(CF₂)_(p)—CH₂OHwherein x and y are each a real number of 0 to 30; z is a real number of0 to 30; w is a real number of 0 to 20; and p is an integer of 1 to 3.Specific examples of fluoropolyether (b) include compounds representedby HOCH₂CF₂CF₂CF₂O(CF₂CF₂CF₂CF₂O)_(w)CF₂CF₂CF₂CH₂OH, compoundsrepresented by HOCH₂CF₂O(CF₂O)_(x)(CF₂CF₂O)_(y)CF₂CH₂OH, and compoundsrepresented by HOCH₂CF₂CF₂O(CF₂CF₂CF₂O)_(z)CF₂CF₂CH₂OH. Thesefluoropolyethers have a number average molecular weight of typically 300to 4000, preferably 500 to 2000, and more preferably 600 to 1500. Thenumber average molecular weight here is a value obtained by measurementof ¹⁹F-NMR with JNM-ECX400 (JEOL Ltd). In NMR measurement, the sampleswere used as they were, without dilution with a solvent. Known peaks,part of the skeleton of the fluoropolyethers, were used as the standardfor chemical shift. Here, x and y are each a real number of 0 to 30, andpreferably a real number of 0 to 12. When x and y are both a real numberof 0 to 12, the molecular chain becomes flat, thereby providing alubricant that can form a thin film; thus it is preferable that x and yare both a real number of 0 to 12. Here, Z is a real number of 0 to 30,and preferably a real number of 1 to 12. When z is a real number of 1 to12, the molecular chain becomes flat, thereby providing a lubricant thatcan form a thin film; thus it is preferable that z is a real number of 1to 12. Here, w is a real number of 0 to 20, and preferably a real numberof 0 to 10. When w is a real number of 0 to 10, the molecular chainbecomes flat, thereby providing a lubricant that can form a thin film;thus it is preferable that w is a real number of 0 to 10. Here, p is aninteger of 1 to 3.

Fluoropolyether (b) has a molecular weight distribution. The molecularweight distribution (PD) represented by weight average molecularweight/number average molecular weight of fluoropolyether (b) is 1.0 to1.5, preferably 1.0 to 1.3, and more preferably 1.0 to 1.1. Themolecular weight distribution is a characteristic value obtained usingHPLC-8220GPC (Tosoh Corporation), a column (PLgel Mixed E, PolymerLaboratories Ltd.), an HCFC-based chlorofluorocarbon alternative as aneluent, and a perfluoropolyether with no functional groups as thestandard substance.

Examples of compound (c) include epoxy-containing compounds, haloalkylalcohols represented by X(CH₂)_(m)OH, and epoxy-containing phenoxycompounds (c-1).

Examples of epoxy-containing compounds include glycidol, propyleneoxide, glycidyl methyl ether, and isobutylene oxide.

In haloalkyl alcohols represented by X(CH₂)_(m)OH, X represents ahalogen atom, such as chlorine, bromine, and iodine, and m is a realnumber of 2 to 8. Examples of haloalkyl alcohols include2-chloroethanol, 3-chloropropanol, 4-chlorobutanol, 5-chloropentanol,6-chlorohexanol, 7-chloroheptanol, 8-chlorooctanol, 2-bromoethanol,3-bromopropanol, 4-bromobutanol, 5-bromopentanol, 6-bromohexanol,7-bromoheptanol, 8-bromooctanol, 2-iodoethanol, 3-iodopropanol,4-iodobutanol, 5-iodopentanol, 6-iodohexanol, 7-iodoheptanol, and8-iodooctanol.

Epoxy-containing phenoxy compound (c-1) is represented, for example, bythe following formula:

Examples of R⁴ includes hydrogen, alkoxy, amino, and an amide residue.

Examples of C₁₋₄ alkoxy include methoxy, ethoxy, propoxy, and butoxy.Examples of amino groups include amino, methylamino, dimethylamino,ethylamino, and diethylamino. Examples of amide residues includeacetamide (—NHCOCH₃) and propionamide (—NHCOC₂H₅).

Specific examples of compound (c-1) include glycidyl 4-methoxyphenylether, glycidyl 4-ethoxyphenyl ether, glycidyl 4-propoxyphenyl ether,glycidyl 4-butoxyphenyl ether, glycidyl 4-aminophenyl ether, glycidyl4-methylaminophenyl ether, glycidyl 4-dimethylaminophenyl ether,glycidyl 4-ethylaminophenyl ether, glycidyl 4-diethylaminophenyl ether,glycidyl 4-acetamidophenyl ether, and glycidyl 4-propionamidephenylether.

For example, the use of HOCH₂CF₂O(CF₂O)_(x)(CF₂CF₂O)_(y)CF₂CH₂OH asfluoropolyether (b) and glycidol as compound (c) generates, throughtheir reaction, HOCH₂CH(OH)CH₂OCH₂CF₂O(CF₂O)_(x)(CF₂CF₂O)_(y)CF₂CH₂OH,HOCH₂CH(OH)CH₂OCH₂CH(OH)CH₂OCH₂CF₂O(CH₂CF₂O)_(y)(CF₂O)_(x)CF₂CH₂OH, andthe like, as fluoropolyether (a).

The use of HOCH₂CF₂O(CF₂O)_(x)(CF₂CF₂O)_(y)CF₂CH₂OH as fluoropolyether(b) and 2-bromoethanol as compound (c) generatesHOCH₂CH₂OCH₂CF₂O(CF₂O)_(x)(CF₂CF₂O)_(y)CF₂CH₂OH as fluoropolyether (a).

The use of HOCH₂CF₂O(CF₂O)_(x)(CF₂CF₂O)_(y)CF₂CH₂OH as fluoropolyether(b) and glycidyl 4-methoxyphenyl ether as compound (c) generatesCH₃O—C₆H₄O—CH₂CH(OH)CH₂OCH₂CF₂O(CF₂O)_(x)(CF₂CF₂O)_(y)CF₂CH₂OH asfluoropolyether (a).

When fluoropolyether (b) is reacted with aliphatic hydrocarbon (A), thefirst step can be skipped, and the following second step is performed.

[2] Subsequently, the compound of the present invention is synthesizedby reacting aliphatic hydrocarbon (A) with fluoropolyether (a) obtainedin the first step or fluoropolyether (b) (second step).

Aliphatic hydrocarbon (A) is reacted with fluoropolyether (a) obtainedin the first step or fluoropolyether (b) in the presence of a base. Thereaction temperature is 20 to 90° C., and preferably 60 to 80° C. Thereaction time is 5 to 20 hours, and preferably 10 to 15 hours. It ispreferable to use 0.5 to 1.5 equivalents of aliphatic hydrocarbon (A)and 0.5 to 2.0 equivalents of a base, relative to fluoropolyether (a) or(b). Bases for use include sodium t-butoxide, potassium t-butoxide,sodium hydroxide, potassium hydroxide, and sodium hydride. The reactioncan be performed in a solvent. Solvents for use include t-Butanol,toluene, and xylene. Thereafter, washing with water and dehydration, forexample, are performed. The compound of the present invention is finallyprovided.

Specific examples of aliphatic hydrocarbon include 1,3-butadienediepoxide, 1,4-pentadiene diepoxide, 1,5-hexadiene diepoxide,1,6-heptadiene diepoxide, 1,7-octadiene diepoxide, 1,8-nonadienediepoxide, 1,9-decane diepoxide, 1,10-undecane diepoxide, 1,11-dodecanediepoxide, and 1,1,1,1-tetra(glycidyl oxymethyl)methane.

Reaction of fluoropolyether (a) obtained in the first step withaliphatic hydrocarbon (A) specifically provides compounds, such asHOCH₂CH(OH)CH₂OCH₂CF₂CF₂O(CF₂CF₂CF₂O)_(z)CF₂CF₂CH₂—OCH₂CH(OH)CH₂CH₂CH₂CH₂CH(OH)CH₂O—CH₂CF₂CF₂O(CF₂CF₂CF₂O)_(z)CF₂CF₂CH₂OCH₂CH(OH)CH₂OHandHOCH₂CH(OH)CH₂OCH₂CF₂CF₂CF₂O(CF₂CF₂CF₂CF₂O)_(w)CF₂CF₂CF₂CH₂—OCH₂CH(OH)CH₂CH₂CH₂CH₂CH(OH)CH₂O—CH₂CF₂CF₂CF₂O(CF₂CF₂CF₂CF₂O)_(w)CF₂CF₂CF₂CH₂OCH₂CH(OH)CH₂OH.

Reaction of fluoropolyether (b) with aliphatic hydrocarbon (A)specifically provides compounds, such asHOCH₂CF₂CF₂O(CF₂CF₂CF₂O)_(z)CF₂CF₂CH₂—OCH₂CH(OH)CH₂CH₂CH₂CH₂CH(OH)CH₂O—CH₂CF₂CF₂O(CF₂CF₂CF₂O)_(z)CF₂CF₂CH₂OHandHOCH₂CF₂CF₂CF₂O(CF₂CF₂CF₂CF₂O)_(w)CF₂CF₂CF₂CH₂—OCH₂CH(OH)CH₂CH₂CH₂CH₂CH(OH)CH₂O—CH₂CF₂CF₂CF₂O(CF₂CF₂CF₂CF₂O)_(w)CF₂CF₂CF₂CH₂OH.

The fluoropolyether compound of the present invention can bind to thesurface of a magnetic disk through at least one hydroxyl group of theC₄₋₁₀ aliphatic hydrocarbon chain present in the middle of the moleculeand at least one polar group present at respective non-hydrocarbon chainterminals of the perfluoropolyethers. In addition, the bonds between thecarbon atoms of the C₄₋₁₀ aliphatic hydrocarbon chain and the oxygenatoms are cleaved by ultraviolet irradiation or heat treatment, andstrong bonds are formed with the surface of the magnetic disk, thusreducing the evaporation of the compound by heat, and maintaining thelubricity of the magnetic disk surface. A lubricant comprising thefluoropolyether compound of the present invention therefore can maintainthe lubricity of the magnetic disk surface at high temperatures underlaser heating.

Before applying the compound of the present invention to the surface ofa magnetic disk, it is preferable to dilute the compound with a solvent.Examples of the solvent include PF-5060, PF-5080, HFE-7100, HFE-7200(3M); and Vertrel-XF (DuPont). The diluted lubricant has a concentrationof 1 wt % or less, and preferably 0.001 to 0.1 wt %.

The compound of the present invention can be used singly, and can alsobe used in combination at any ratio with a fluoropolyether-basedlubricant typically used in lubricants for magnetic disks, such asFomblin Ztetraol, Zdol TX, AM, (Solvay Solexis), Demnum (DaikinIndustries, Ltd.), and Krytox (Dupont).

The compound of the present invention can be used as a lubricant toreduce the spacing between a magnetic disk and a head inside a magneticdisk apparatus and improve the durability against sliding. The lubricantof the present invention has excellent heat resistance, and is thussuitable for magnetic disks in hard disk drives (HDD) using an HAMRtechnique. Thus, the compound is usable for not only magnetic disks, butalso magnetic heads, photomagnetic recording devices, and magnetictapes, all three of which have a carbon protective film, surfaceprotective films for organic materials, such as plastics, and surfaceprotective films for inorganic materials, such as Si₃N₄, SiC, and SiO₂.

FIG. 1 is a cross-sectional diagram showing a magnetic disk according tothe present invention. The magnetic disk of the present inventioncomprises a recording layer 2 formed on a substrate 1, a protectivelayer 3 formed on the recording layer 2, and a lubricant layer 4, whichcomprises the compound of the present invention and a lubricant formagnetic disks, formed on the protective layer 3 as the outermost layer.Examples of the substrate 1 include aluminium alloys, ceramics such asglass, and polycarbonate. The recording layer 2 may comprise 2 or morelayers.

Examples of constituent materials for a magnetic layer, which is therecording layer of the magnetic disk, include primarily elements capableof forming a ferromagnet, such as iron, cobalt, and nickel; alloyscontaining chromium, platinum, tantalum, or the like in addition to suchelements; and oxides thereof. The layer of these materials is formed bya technique such as plating and sputtering. Examples of materials forthe protective layer include SiC and SiO₂. The layer of these materialsis formed by sputtering or CVD.

Lubricant layers presently available have a thickness of 30 Å or less.When a lubricant having a viscosity of about 100 mPa·s or more at 20° C.is applied as it is, the resulting film could have an excessively largethickness. Thus, such a lubricant is dissolved in a solvent for use incoating. In either case where the compound of the present invention isused as a lubricant singly or mixed with other lubricants, the lubricantof the present invention dissolved in a solvent makes it easier todesirably control the film thickness. However, the concentration variesdepending on the coating technique and conditions, the mixing ratio, andthe like. The thickness of a film formed by the lubricant of the presentinvention is preferably 5 to 15 Å.

To form a strong bond between the lubricant and the magnetic disk, it ispreferable to, after applying the lubricant to the surface of themagnetic disk, subject the surface of the magnetic disk to ultravioletirradiation or heat treatment. When performing ultraviolet irradiation,it is preferable to use ultraviolet rays having a wavelength of 185 nmor 254 nm as the dominant wavelength. The temperature of the heattreatment is preferably about 120 to 170° C. Performing ultravioletirradiation or heat treatment can further reduce the evaporation of thelubricant by heat.

A preferable magnetic disk of the present invention comprises insequence over a substrate, a recording layer, a protective layer, and alubricant layer, wherein the lubricant layer is formed by applying thefluoropolyether-containing lubricant to the surface of the protectivelayer, and performing ultraviolet irradiation or heat treatment.

The method for producing this magnetic disk includes a method forproducing a magnetic disk that comprises in sequence over a substrate, arecording layer, a protective layer, and a lubricant layer, and themethod comprises forming a recording layer and a protective layer over asubstrate in this order, applying the fluoropolyether-containinglubricant to the surface of the protective layer, and performingultraviolet irradiation or heat treatment to form a lubricant layer.

The magnetic disk of the present invention can be used in a magneticdisk apparatus that comprises: a magnetic disk drive that stores thedisk, and that is equipped with a magnetic head for recording,reproducing, and erasing information, a motor for rotating the disketc.; and a control system for controlling the drive.

The magnetic disk according to the present invention and a magnetic diskapparatus comprising the magnetic disk can be used, for example, as anexternal memory for computers, word processors etc. The disk andapparatus can also be used in various devices, such as navigationsystems, game consoles, cellular phones, and PHS; internal or externalrecording devices for building security, power plant administrationsystems, power plant control systems; and the like.

EXAMPLES

The following Examples will describe the present invention in detail.However, the present invention is not limited to the Examples. Note that¹⁹F-NMR was measured without a solvent, and using as the standardchemical shift a known peak that is a portion of the backbone structureof a fluoropolyether, and that ¹H-NMR was measured without a solvent andusing D₂O as the standard substance.

Example 1

Synthesis ofHOCH₂CH(OH)CH₂OCH₂CF₂CF₂O(CF₂CF₂CF₂O)_(z)CF₂CF₂CH₂—OCH₂CH(OH)CH₂CH₂CH₂CH₂CH(OH)CH₂O—CH₂CF₂CF₂O(CF₂CF₂CF₂O)_(z)CF₂CF₂CH₂OCH₂CH(OH)CH₂OH(Compound 1)

In an argon atmosphere, a mixture of t-butyl alcohol (41 g), 95 g of afluoropolyether represented by HO—CH₂CF₂CF₂O(CF₂CF₂CF₂O)_(z)CF₂CF₂CH₂—OH(the number average molecular weight: 1980, the molecular weightdistribution: 1.25), potassium t-butoxide (0.6 g), and glycidol (3.6 g)was stirred at 70° C. for 14 hours. Subsequently, the mixture was washedwith water, dehydrated, and purified by silica gel columnchromatography, thereby giving 95 g of a perfluoropolyether having onehydroxyl group at one terminal and two hydroxyl groups at the otherterminal (the average molecular weight: 2110). This compound (95 g) wasdissolved in meta-xylene hexafluoride (95 g), and sodium hydroxide (3.0g) and 1,7-octadienediepoxide (3.2 g) were added thereto, followed bystirring at 70° C. for 14 hours. The mixture was then washed with water,dehydrated, and purified by distillation, thereby giving 60 g ofcompound 1.

Compound 1 was a colorless transparent liquid, and had a density of 1.74q/cm³ at 20° C. Compound 1 was identified by NMR as shown below.

¹⁹F-NMR (solvent: none, standard substance: OCF₂CF₂ CF₂O in the obtainedproduct, which was taken as −129.7 ppm)

δ=−129.7 ppm

[18F, —OCF₂CF₂ CF₂O—],

δ=−83.7

[36F, —OCF₂ CF₂CF₂ O—],

δ=−124.2 ppm

[8F, —OCF₂ CF₂CH₂OCH₂CH(OH)CH₂CH₂CH₂CH₂CH(OH)CH₂—, —OCF₂CF₂CH₂OCH₂CH(OH)CH₂OH],

δ=−86.5 ppm

[8F, —OCF₂ CF₂CH₂OCH₂CH(OH)CH₂CH₂CH₂CH₂CH(OH)CH₂—, —OCF₂CF₂CH₂OCH₂CH(OH)CH₂O],

z=9.3

¹H-NMR (solvent: none, standard substance: D₂O)

δ=3.2 to 3.8 ppm

[30H, HOCH₂ CH(OH)CH₂ OCH₂ CF₂CF₂O(CF₂CF₂CF₂O)_(z)CF₂CF₂CH₂ —OCH₂CH(OH)CH₂CH₂CH₂CH₂CH(OH)CH₂ O—CH₂ CF₂CF₂O(CF₂CF₂CF₂O)_(z)CF₂CF₂CH₂ OCH₂CH(OH)CH₂ OH]

δ=1.1 ppm.

[8H, HOCH₂CH(OH)CH₂OCH₂CF₂CF₂(CF₂CF₂CF₂O)_(z)CF₂CF₂CH₂—OCH₂CH(OH)CH₂ CH₂CH₂ CH₂ CH(OH)CH₂O—CH₂CF₂CF₂O(CF₂CF₂CF₂O)_(z)CF₂CF₂CH₂OCH₂CH(OH)CH₂OH]

Example 2

Synthesis ofHOCH₂CH(OH)CH₂OCH₂CF₂CF₂CF₂O(CF₂CF₂CF₂CF₂O)_(w)CF₂CF₂CF₂CH₂—OCH₂CH(OH)CH₂CH₂CH₂CH₂CH(OH)O—CH₂CF₂CF₂CF₂O(CF₂CF₂CF₂CF₂O)_(w)CF₂CF₂CF₂CH₂OCH₂CH(OH)CH₂OH(Compound 2)

The procedure of Example 1 was repeated except that a fluoropolyetherrepresented by HO—CH₂CF₂CF₂O(CF₂CF₂CF₂CF₂O)_(w)CF₂CF₂CF₂—CH₂—OH was usedinstead of the fluoropolyether represented byHO—CH₂CF₂CF₂O(CF₂CF₂CF₂O)_(z)CF₂CF₂CH₂—OH used in Example 1, therebygiving 58 g of compound 2.

Compound 2 was a colorless transparent liquid, and had a density of 1.77g; cm³ at 20° C. Compound 2 was identified by NMR as shown below.

¹⁹F-NMR (solvent: none, standard substance: OCF₂CF₂ CF₂ CF₂O in theobtained product, which was taken as −125.8 ppm)

δ=−83.7 ppm

[32F, —OCF₂ CF₂CF₂CF₂ O—, —OCF₂CF₂CF₂CH₂OCH₂CH(OH)CH₂CH₂CH₂CH₂CH(OH)CH₂—, —OCF₂CF₂CF₂CH₂OCH₂CH(OH)CH₂OH],

δ=−120.5 ppm

[12F, —OCF₂CF₂ CF₂CH₂OCH₂CH(OH)CH₂CH₂CH₂CH₂CH(OH)CH₂—, —OCF₂ CF₂CF₂CH₂OCH₂CH(OH)CH₂OH],

δ=−125.8 ppm

[24F, —OCF₂CF₂ CF₂ CF₂O—],

δ=−127.6 ppm

[8F, —OCF₂CF₂ CF₂CH₂OCH₂OH(OH)CH₂CH₂CH₂CH₂CH(OH)CH₂—, —OCF₂CF₂CF₂CH₂OCH₂CH(OH)CH₂OH]

w=3.0

¹H-NMR (solvent: none, standard substance: D₂O)

δ=3.2 to 3.8 ppm

[30H, HOCH₂ CH(OH)CH₂ OCH₂ CF₂CF₂CF₂O(CF₂CF₂CF₂CF₂O)_(w)CF₂CF₂CF₂CH₂—OCH₂ CH(OH)CH₂CH₂CH₂CH₂CH(OH)CH₂ O—CH₂CF₂CF₂CF₂O(CF₂CF₂CF₂CF₂O)_(w)CF₂CF₂CF₂CH₂ OCH₂ CH(OH)CH₂ OH]

δ=1.1 ppm

[8H, HOCH₂CH(OH)CH₂OCH₂CF₂CF₂CF₂O(CF₂CF₂CF₂CF₂O)_(w)CF₂CF₂CF₂CH₂—OCH₂CH(OH)CH₂ CH₂CH₂ CH₂CH(OH)CH₂O—CH₂CF₂CF₂CF₂O(CF₂CF₂CF₂CF₂O)_(w)CF₂CF₂CF₂CH₂OCH₂CH(OH)CH₂OH]

Example 3

Synthesis ofHOCH₂CF₂CF₂O(CF₂CF₂CF₂O)_(z)CF₂CF₂CH₂—OCH₂CH(OH)CH₂CH₂CH₂CH₂CH(OH)CH₂O—CH₂CF₂CF₂O(CF₂CF₂CF₂O)_(z)CF₂CF₂CH₂OH(Compound 3)

In an argon atmosphere, 80 g of a fluoropolyether represented byHO—CH₂CF₂CF₂O(CF₂CF₂CF₂O)_(z)CF₂CF₂CH₂—OH (the number average molecularweight: 1890, the molecular weight distribution: 1.20) was dissolved inmeta-xylene hexafluoride (80 g), and sodium hydroxide (2.4 g) and1,7-octadienediepoxide (2.6 g) were added thereto, followed by stirringat 70° C. for 14 hours. The mixture was then washed with water,dehydrated, and purified by distillation, thereby giving 55 g ofcompound 3.

Compound 3 was a colorless transparent liquid, and had a density of 1.70g/cm³ at 20° C. Compound 3 was identified by NMR as shown below.

¹⁹F-NMR (solvent: none, standard substance: OCF₂CF₂ CF₂O in the obtainedproduct, which was taken as −129.7 ppm)

δ=−129.7 ppm

[36F, —OCF₂CF₂ CF₂O—],

δ=−83.7

[72F, —OCF₂ CF₂CF₂ O—],

δ=−124.2 ppm

[4F, —OCF₂ CF₂CH₂OCH₂CH(OH)CH₂CH₂CH₂CH₂CH(OH)CH₂—],

δ=−126.4 ppm

[4F, —OCF₂ CF₂CH₂OH],

δ=−86.5 ppm

[8F, —OCF₂CF₂ CH₂OCH₂CH(OH)CH₂CH₂CH₂CH₂CH(OH)CH₂—, —OCF₂CF₂CH₂OCH₂CH(OH)CH₂OH]

z=9.1

¹H-NMR (solvent: none, standard substance: D₂O)

δ=3.2 to 3.8 ppm

[18H, HOCH₂ CF₂CF₂O(CF₂CF₂CF₂O)_(z)CF₂CF₂CH₂ —OCH₂CH(OH)CH₂CH₂CH₂CH(OH)CH₂ O—CH₂ O(CF₂CF₂CF₂O)_(z)CF₂CF₂CH₂ OH]

δ=1.1 ppm

[8H, HOCH₂CF₂O(CF₂CF₂CF₂O)_(z)CF₂CF₂CH₂—OCH₂CH(OH)CH₂ CH₂ CH₂ CH₂CH(OH)CH₂O—CH₂CF₂CF₂O(CF₂CF₂CF₂O)_(z)CF₂CF₂CH₂OH]

Example 4

Synthesis ofHOCH₂CF₂CF₂CF₂O(CF₂CF₂CF₂CF₂O)_(w)CF₂CF₂CF₂CH₂—OCH₂CH(OH)CH₂CH₂CH₂CH₂CH(OH)CH₂O—CH₂CF₂CF₂CF₂O(CF₂CF₂CF₂CF₂O)_(w)CF₂CF₂CF₂CH₂OH(Compound 4)

The procedure of Example 3 was repeated except that a fluoropolyetherrepresented by HO—CH₂CF₂CF₂O(CF₂CF₂CF₂CF₂O)_(w)CF₂CF₂CF₂—CH₂—OH was usedinstead of the fluoropolyether represented byHO—CH₂CF₂CF₂O(CF₂CF₂CF₂O)_(z)CF₂CF₂CH₂—OH used in Example 3, therebygiving 45 g of compound 4.

Compound 4 was a colorless transparent liquid, and had a density of 1.72g/cm³ at 20° C. Compound 4 was identified by NMR as shown below.

¹⁹H-NMR (solvent none, standard substance: OCF₂CF₂CF₂CF₂O in theobtained product, which was taken as −125.8 ppm)

δ=−83.7 ppm

[32F, —OCF₂ CF₂CF₂CF₂ O, —OCF₂CF₂CF₂CH₂OCH₂CH(OH)CH₂CH₂CH₂CH₂CH(OH)CH₂—, —OCF₂ CF₂CF₂CH₂OH],

δ=−120.5 ppm

[4F, —OCF₂CF₂CF₂ CH₂OCH₂CH(OH)CH₂CH₂CH₂CH₂CH(OH)CH₂—],

δ=−122.8 ppm

[4F, —OCF₂CF₂CF₂ CH₂OH],

δ=−125.8 ppm

[24F, —OCF₂CF₂ CF₂ O—],

δ=−127.6 ppm

[8F, —OCF₂CF₂ CF₂OCH₂CH(OH)CH₂CH₂CH₂CH(OH)CH₂—, —OCF₂CF₂CF₂CH₂CH(OH)CH₂OH]

w=3.0

¹H-NMR (solvent: none, standard substance: D₂O)

δ=3.2 to 3.8 ppm

[18H, HOCH₂ CF₂CF₂CF₂O(CF₂CF₂CF₂CF₂O)_(w)CF₂CF₂CF₂CH₂ —OCH₂CH(OH)CH₂CH₂CH₂CH₂CH(OH)CH₂ O—CH₂ CF₂CF₂CF₂O(CF₂CF₂CF₂CF₂O)_(w)CF₂CF₂CH₂OH]

δ=1.1 ppm

[8H, HOCH₂CF₂CF₂CF₂O(CF₂CF₂CF₂CF₂O)_(w)CF₂CF₂CF₂CH₂—OCH₂CH₂(OH)CH₂ CH₂CH₂ CH₂ CH(OH)CH₂O—CH₂CF₂CF₂O(CF₂CF₂CF₂O)_(w)CF₂CF₂CF₂CH₂OH]

For comparison, the following compounds 5 to 7 were used.

Compound 5 isHOCH₂CH(OH)CH₂OCH₂CF₂O(CF₂O)_(x)(CF₂CF₂O)_(y)CF₂CH₂OCH₂CH(OH)CH₂OCH₂CF₂O(CF₂O)_(x)(CF₂CF₂O)_(y)CF₂CH₂OCH₂CH(OH)CH₂OH,which was produced in accordance with the following production method.

In an argon atmosphere, a mixture of t-butyl alcohol (39 g), 90 g of afluoropolyether represented by HO—CH₂CF₂O(CF₂O)_(x)(CF₂CF₂)_(y)CF₂CH₂—OH(the number average molecular weight: 1350, the molecular weightdistribution: 1.25), potassium t-butoxide (0.7 g), and glycidol (5 g)was stirred at 70° C. for 14 hours. The mixture was then washed withwater, dehydrated, and purified by silica gel column chromatography,thereby giving a compound having one hydroxyl group at one terminal andtwo hydroxyl groups at the other terminal. This compound (85 g) wasdissolved in t-butyl alcohol (57 g), and potassium t-butoxide (3.6 g)and epichlorohydrin (3.7 g) were added thereto, followed by stirring at70° C. for 14 hours. The mixture was then washed with water, dehydrated,and purified by distillation, thereby giving 60 g of compound 5.

Compound 5 was a colorless transparent liquid, and had a density of 1.74g/cm³ at 20° C. Compound 5 was identified by NMR as shown below.

¹⁹F-NMR (solvent: none, standard substance: OCF₂CF₂ CF₂ CF₂O in theobtained product, which was taken as −125.8 ppm)

δ=−52.1 ppm, −53.7 ppm, −55.4 ppm

[24F, —OCF₂ O—],

δ=−89.1 ppm, −90.7 ppm

[48F, —OCF₂ CF₂ O—],

δ=−77.9 ppm, −80.0 ppm

[8F, —OCF₂ CH₂OCH₂CH(OH)CH₂O—, —OCF₂ CH₂OCH₂CH(OH)CH₂OH],

x=6.2, y=6.1

¹⁹H-NMR (solvent: none, standard substance: D₂O)

δ=3.2 to 3.8 ppm

[28H, HOCH₂ CH(OH)CH₂ OCH₂ —CF₂O(CF₂O)_(x)(CF₂CF₂O)_(y)CF₂CH₂ , —O—CH₂CH(OH)CH₂ O—]

Compound 6 is a compound represented byHOCH₂CH(OH)CH₂OCH₂CF₂O(CF₂CF₂O)_(x)(CF₂O)_(y)CF₂CH₂OCH₂CH(OH)CH₂OH, andis also called Fomblin Ztetraol (produced by Solvey Solexis, tradename), which is a typical lubricant for magnetic disks. Compound 6 wasproduced in accordance with the following production method.

In an argon atmosphere, a mixture of t-butyl alcohol (39 g), 91 g of afluoropolyether represented byHO—CH₂CF₂O(CF₂CF₂O)_(x)(CF₂O)_(y)CF₂CH₂—OH (the number average molecularweight: 2:393, the molecular weight distribution: 1.32), potassiumt-butoxide (0.7 g), and glycidol (10 g) was stirred at 70° C. for 14hours. The mixture was then washed with water, dehydrated, and purifiedby silica gel column chromatography, thereby giving 82 g of compound 6having two hydroxyl groups at each terminal (the average molecularweight: 2432).

Compound 6 was a colorless transparent liquid, and had a density of 1.73g/cm³ at 20° C. Compound 6 was identified by NMR as shown below.

¹⁹F-NMR (solvent: none, standard substance: OCF₂CF₂ CF₂ CF₂O in theobtained product, which was taken as −125.8 ppm)

δ=−52.1 ppm, −53.7 ppm, −55.4 ppm

[24F, —OCF₂ O—],

δ=−89.1 ppm, −90.7 ppm

[48F, —OCF₂ CF₂ O—],

δ=−77.9 ppm, −80.0 ppm

[4F, —OCF₂ CH₂OCH₂CH(OH)CH₂OH],

x=12.1, y=12.3

¹H-NMR (solvent: none, standard substance: D₂O)

δ=3.2 to 3.8 ppm

[18H, HOCH₂ CH(OH)CH₂ OCH₂ —CF₂O(CF₂CF₂O)_(x)(CF₂O)_(y)CF₂CH₂ —O—CH₂CH(OH)CH₂ OH]

Compound 7 is a compound represented by formula (5)(HOCH₂CH(OH)CH₂OCH₂CF₂CF₂O(CF₂CF₂CF₂O)_(n)CF₂CF₂CH₂OCH₂OH(OH)CH₂OH)disclosed in paragraph [0004] of Patent Literature 2 (WO2009/066784).Compound 7 was produced in accordance with the following productionmethod, and had two hydroxyl groups at each terminal of the molecule.

In an argon atmosphere, a mixture of t-butyl alcohol (41 g), 95 g of afluoropolyether represented by HO—CH₂CF₂CF₂O(CF₂CF₂CF₂O)_(n)CF₂CF₂CH₂—OH(the number average molecular weight: 1850, the molecular weightdistribution: 1.25), potassium t-butoxide (0.8 g), and glycidol (11 g)was stirred at 70° C. for 14 hours. The mixture was then washed withwater, dehydrated, and purified by silica gel column chromatography,thereby giving 90 g of compound 7 having two hydroxyl groups at eachterminal (the average molecular weight: 1936).

Compound 7 was a colorless transparent liquid, and had a density of 1.75g/cm³ at 20° C. Compound 7 was identified by NMR as shown below.

¹⁹F-NMR (solvent: none, standard substance: OCF₂CF₂ CF₂O in the obtainedproduct, which was taken as −129.7 ppm)

δ=−129.7 ppm

[26F, —OCF₂CF₂ CF₂O—],

δ=−83.7

[52F, —OCF₂ CF₂CF₂ O—],

δ=−124.2 ppm

[4F, —OCF₂ CF₂CH₂OCH₂CH(OH)CH₂OH],

δ=−86.5 ppm.

[4F, —OCF₂CF₂ CH₂OCH₂CH(OH)CH₂OH]

n=13.0

¹H-NMR (solvent: none, standard substance: D₂O)

δ=3.2 to 3.8 ppm

[18H, HO—CH₂ CH(OH)CH₂ O—CH₂ CF₂CF₂O(CF₂CF₂CF₂O)_(n)CF₂CF₂CH₂ —O—CH₂CH(OH)CH₂ OH]

Test Example 1: Measurement of Bonding Rate

Each compound was dissolved in Vertrel-XF, product of DuPont, to preparea lubricant. A magnetic disk, 2.5 inches in diameter, was immersed inthe solution for 1 minute and then withdrawn at a rate of 2 mm/s. Thedisk coated with the lubricant was then inserted into an ultravioletirradiator equipped with a low-pressure mercury lamp that emitsultraviolet rays at a wavelength of 185 nm and 254 nm, and maintainedfor 10 to 20 seconds. To prevent ozone formation, the inside of theultraviolet irradiator had been replaced with nitrogen beforehand. Theaverage film thickness of the compound on the disk was then measured bya Fourier Transform Infrared Spectrometer (FT-IR). This film thicknesswas taken as fÅ. Subsequently, the disk was immersed in a mixed solventof Vertrel-XF and methanol (a volume ratio of 70:30) for 5 minutes,withdrawn at a rate of 2 mm/s, and allowed to stand at room temperaturefor volatilization of the solvent. The average film thickness of thecompound remaining on the disk was measured with FT-IR, and the film,thickness was taken as bÅ. The bonding rate, which is typically used,was used as an indicator to show the degree of adsorption of thelubricant to the disk. The bonding rate is expressed by the followingequation.Bonding Rate (%)=100×b/f

TABLE 1 Compound 1 Compound 2 Compound 3 Compound 4 Compound 5 Compound6 Compound 7 Bonding 48 50 46 48 36 35 29 Rate (%)

Table 1 shows that compounds 1 to 4 of the present in have higherbonding rates than compounds 5 to 7, which are Comparative Examples.

Test Example 2: Evaluation of Decomposition Using Ultraviolet Irradiatorand Thermal Analyzer (TG/TDA)

0.3 g of each compound was individually placed in a Petri dish, andirradiated with an ultraviolet irradiator (wavelength 185 nm and 254 nm)in a nitrogen atmosphere for 6 hours. Compounds 1 to 7 beforeultraviolet irradiation and compounds 1 to 7 after ultravioletirradiation were heated at a temperature increase rate of 2° C./min in anitrogen atmosphere, and the temperature at which the weight of eachcompound decreased by 10% was measured with a thermal analyzer (TG/TDA).The samples before ultraviolet irradiation and the samples afterultraviolet irradiation were compared in terms of the temperatures atwhich they lost their 10% weight to evaluate the decomposition of thecompounds.

TABLE 2 Compound 1 Compound 2 Compound 3 Compound 4 Compound 5 Compound6 Compound 7 Before UV 297 305 279 294 294 234 280 Irradiation (° C.)After UV 253 260 256 252 292 236 275 Irradiation (° C.)

Table 2 shows that whereas the temperature at which weight decreaseoccurred did not change before and after ultraviolet irradiation in thecase of compounds 5 to 7 (i.e., Comparative Examples), the lubricants ofcompounds 1 to 4 of the present invention exposed to ultravioletirradiation decomposed and scattered at temperatures lower than thetemperatures at which compounds 1 to 4 decomposed before exposure toultraviolet irradiation. This indicates that ultraviolet irradiation tocompounds 1 to 4 of the present invention cleaved the bonds between thecarbon atoms of the C₄₋₁₀ aliphatic hydrocarbon chain present in themiddle of the molecule and the oxygen atoms to thereby generatecompounds having a lower molecular weight, which evaporated at a lowertemperature than before ultraviolet irradiation. Compounds 5 to 7,however, do not contain a C₄₋₁₀ aliphatic hydrocarbon chain in themiddle of the molecule, and such cleavage of ether linkage did not occurunder ultraviolet irradiation, thus resulting in substantially no changein temperature at which the weight of the compound decreased betweenbefore and after ultraviolet irradiation.

The results suggest that the compound of the present inventioncontaining a C₄₋₁₀ aliphatic hydrocarbon chain in the middle of themolecule is cleaved between the carbon atoms of the C₄₋₁₀ aliphatichydrocarbon chain and the oxygen atoms by ultraviolet irradiation, andthe portions where ether linkages are cleaved bind to the surface of themagnetic disk, enhancing the bonding rate.

DESCRIPTION OF THE REFERENCE NUMERALS

-   1 substrate-   2 recording layer-   3 protective layer-   4 lubricant layer

The invention claimed is:
 1. A fluoropolyether compound comprising (i) aC₄₋₁₀ aliphatic hydrocarbon chain present in the middle of thefluoropolyether compound and (ii) at least two perfluoropolyethers, eachperfluoropolyether being ether-linked to the C₄₋₁₀ aliphatic hydrocarbonchain, the C₄₋₁₀ aliphatic hydrocarbon chain having at least onehydroxyl group, the at least two perfluoropolyethers having, atrespective non-hydrocarbon chain terminals, at least one polar groupselected from the group consisting of —OH, —OCH₂CH(OH)CH₂OH,—OCH₂CH(OH)CH₂OCH₂CH(OH)CH₂OH, —O(CH₂)_(m)OH, and—OCH₂(OH)CHCH₂—OC₆H₄—R¹, wherein m is an integer of 2 to 8, and R¹represents hydrogen, C₁₋₄ alkoxy, amino, or an amide residue.
 2. Thefluoropolyether compound according to claim 1, wherein the C₄₋₁₀aliphatic hydrocarbon chain has 8 carbon atoms.
 3. The fluoropolyethercompound according to claim 1, which is at least one member selectedfrom the group consisting ofHOCH₂CH(OH)CH₂OCH₂CF₂CF₂O(CF₂CF₂CF₂O)_(z)CF₂CF₂CH₂—OCH₂CH(OH)CH₂CH₂CH₂CH₂CH(OH)CH₂O—CH₂CF₂CF₂O(CF₂CF₂CF₂O)_(z)CF₂CF₂CH₂OCH₂CH(OH)CH₂OH,wherein z is a real number of 0 to 30,HOCH₂CH(OH)CH₂OCH₂CF₂CF₂CF₂O(CF₂CF₂CF₂CF₂O)_(w)CF₂CF₂CF₂CH₂—OCH₂CH(OH)CH₂CH₂CH₂CH₂CH(OH)CH₂O—CH₂CF₂CF₂CF₂O(CF₂CF₂CF₂CF₂O)_(w)CF₂CF₂CF₂CH₂OCH₂CH(OH)CH₂OH,wherein w is a real number of 0 to 20,HOCH₂CF₂CF₂O(CF₂CF₂CF₂O)_(z)CF₂CF₂CH₂—OCH₂CH(OH)CH₂CH₂CH₂CH₂CH(OH)CH₂O—CH₂CF₂CF₂O(CF₂CF₂CF₂O)_(z)CF₂CF₂CH₂OH,wherein z is a real number of 0 to 30, andHOCH₂CF₂CF₂CF₂O(CF₂CF₂CF₂CF₂O)_(w)CF₂CF₂CF₂CH₂—OCH₂CH(OH)CH₂CH₂CH₂CH₂CH(OH)CH₂O—CH₂CF₂CF₂CF₂O(CF₂CF₂CF₂CF₂O)_(w)CF₂CF₂CF₂CH₂OH,wherein w is a real number of 0 to
 20. 4. A lubricant comprising thefluoropolyether compound according to claim
 1. 5. A magnetic diskcomprising, in sequence over a substrate: a recording layer, aprotective layer, and a lubricant layer, wherein the lubricant layer isformed by applying the lubricant according to claim 4 to the surface ofthe protective layer, and performing ultraviolet irradiation or heattreatment.
 6. A method for producing a magnetic disk that comprises insequence over a substrate, a recording layer, a protective layer, and alubricant layer, the method comprising forming the recording layer andthe protective layer over the substrate in this order, applying thelubricant according to claim 4 to the surface of the protective layer,and performing ultraviolet irradiation or heat treatment to form thelubricant layer.
 7. The fluoropolyether compound according to claim 2,which is at least one member selected from the group consisting ofHOCH₂CH(OH)CH₂OCH₂CF₂CF₂O(CF₂CF₂CF₂O)_(z)CF₂CF₂CH₂—OCH₂CH(OH)CH₂CH₂CH₂CH₂CH(OH)CH₂O—CH₂CF₂CF₂O(CF₂CF₂CF₂O)_(z)CF₂CF₂CH₂OCH₂CH(OH)CH₂OH,wherein z is a real number of 0 to 30,HOCH₂CH(OH)CH₂OCH₂CF₂CF₂CF₂O(CF₂CF₂CF₂CF₂O)_(w)CF₂CF₂CF₂CH₂—OCH₂CH(OH)CH₂CH₂CH₂CH₂CH(OH)CH₂O—CH₂CF₂CF₂CF₂O(CF₂CF₂CF₂CF₂O)_(w)CF₂CF₂CF₂CH₂OCH₂CH(OH)CH₂OHwherein w is a real number of 0 to 20,HOCH₂CF₂CF₂O(CF₂CF₂CF₂O)_(z)CF₂CF₂CH₂—OCH₂CH(OH)CH₂CH₂CH₂CH₂CH(OH)CH₂O—CH₂CF₂CF₂O(CF₂CF₂CF₂O)_(z)CF₂CF₂CH₂OH,wherein z is a real number of 0 to 30, andHOCH₂CF₂CF₂CF₂O(CF₂CF₂CF₂CF₂O)_(w)CF₂CF₂CF₂CH₂—OCH₂CH(OH)CH₂CH₂CH₂CH₂CH(OH)CH₂O—CH₂CF₂CF₂CF₂O(CF₂CF₂CF₂CF₂O)_(w)CF₂CF₂CF₂CH₂OH,wherein w is a real number of 0 to
 20. 8. A lubricant comprising thefluoropolyether compound according to claim
 2. 9. The fluoropolyethercompound according to claim 1, wherein the at least twoperfluoropolyethers comprises, at respective non-hydrocarbon chainterminals, —OH, —OCH₂CH(OH)CH₂OH.
 10. The fluoropolyether compoundaccording to claim 1, wherein the at least two perfluoropolyetherscomprises, at respective non-hydrocarbon chain terminals,—OCH₂CH(OH)CH₂OCH₂CH(OH)CH₂OH.
 11. The fluoropolyether compoundaccording to claim 1, wherein the at least two perfluoropolyetherscomprises, at respective non-hydrocarbon chain terminals, —O(CH₂)_(m)OH,and —OCH₂(OH)CHCH₂—OC₆H₄—R¹.
 12. The fluoropolyether compound accordingto claim 1, wherein R¹ is hydrogen.
 13. The fluoropolyether compoundaccording to claim 1, wherein R¹ is C₁₋₄ alkoxy.
 14. The fluoropolyethercompound according to claim 1, wherein R¹ is amino.
 15. Thefluoropolyether compound according to claim 1, wherein R¹ is an amideresidue.
 16. The fluoropolyether compound according to claim 3, whereinz is not 0, and w is not
 0. 17. The fluoropolyether compound accordingto claim 3, wherein z is a real number of 2 to 8, and w is a real numberof 1 to 5.